Put input sources for bevy_input under features

[Shatur]

Objective

bevy_input provides primitives for all kinds of input. But on consoles you usually don't have things like touch. On more obscure platforms, like GBA, only gamepad input is needed.

Solution

To avoid including extra stuff, I put each source under a feature. I didn't enable them by default to avoid typing

default-features = false, features = [
    "std",
    "bevy_reflect",
    "bevy_ecs/async_executor",
    "smol_str"
]

in all places that include bevy_input. Instead, I just enabled the used input sources in bevy_window and bevy_gilrs. This way, when a crate that provides hardware support for a specific input source is not used, the corresponding feature in bevy_input also won't be enabled.

For GBA this reduced the binary size for the game example from 1.6M to 1.4M.

Considered alternatives

I also considered doing something like this:

pub struct InputPlugin {
    pub keyboard: bool,
    pub mouse: bool,
    pub gamepad: bool,
    pub touch: bool,
}

But this doesn't eliminate extra code even with LTO enabled and might be confusing for users, since toggling these values could cause a crash due to a missing resource when a crate like bevy_window expects it.

[alice-i-cecile]

I like this change. That space savings is nothing to sneeze at on embedded, and this feels like the cleanest way to do this. Some platforms / projects genuinely don't need various input modes.

The features aren't set up quite right: you need descriptions over each individual feature and then you'll need to regenerate a file. See #21434 for details.

in all places that include bevy_input. Instead, I just enabled the used input sources in bevy_window and bevy_gilrs. This way, when a crate that provides hardware support for a specific input source is not used, the corresponding feature in bevy_input also won't be enabled.

I was expecting default features to be enabled for these, but your explanation here makes sense and seems fine to me.

Oh and this also needs a solid migration guide: changes to features are really hard to debug!

[Shatur]

Yep, I'm already working on all of these!